1. Field of the Invention
This invention pertains to electron guns for devices such as cathode ray tubes (CRTs). More particularly, a package structure for mounting a field-emitting device into an electron gun is provided.
2. Description of Related Art
A cathode ray tube (CRT) and other devices requiring an electron beam normally include an electron gun having a thermionic emitter as the cathode. The electron gun is assembled to include the cathode and other electrodes that focus and accelerate the electron beam. Such electron guns are typically assembled manually and the cathode is inserted after the gun is assembled. Such assembly can be costly. It would be an advantage to include the cathode portion of the gun in the initial assembly.
The technology to allow replacement of cathodes based on thermionic emission with cold cathodes based on field emission of electrons has been developing in recent years. The field emission of electrons occurs from microtips that are fabricated from molybdenum, silicon or, in very recent years, carbon-based materials. It has been demonstrated that the carbon-based material or diamond-like material can be monolithically integrated with gated electrodes in a self-aligned structure, using integrated circuit fabrication techniques (xe2x80x9cAdvanced CVD Diamond Microtip Devices for Extreme Applications,xe2x80x9d MAT. RES. SOC. SYMP. PROC., Vol. 509 (1998)). The use of field emission devices with the extraction gate built-in eliminates the need for two of the electrodes in an electron gun built on thermionic emission. Elimination of these components simplifies the gun and also reduces its length. The application of the integrated carbon-like cathode and electrodes into an electron gun has been described in pending and commonly assigned patent application entitled xe2x80x9cCompact Field Emission Electron Gun and Focus Lens,xe2x80x9d filed Jul. 19, 1999, Ser. No. 09/356,851, with named inventors Rich Gorski and Keith D. Jamison, which is incorporated herein by reference.
Devices heretofore known for assembling cathode structures and electron guns using field emission cathodes are described in U.S. Pat. No. 5,898,262. This patent describes a way for packaging a field-emitting device to construct a color cathode ray tube. An insulating piece with an indentation for a single field emitting device that has three emission areas is provided. U.S. Pat. No. 5,869,924 provides an insulating material (plastic) that is created by filling in an external case, with pins extending through the insulating material. The cathode device is wire-bonded directly to the head of the pins. U.S. Pat. No. 5,905,332 discloses additional portions of an electron gun beyond the field-emitting cathode itself. The aperture spacing in the focusing portion of the gun is larger than the spacing between the field emitting devices.
The cathode, accelerating and focusing elements of electron guns may be assembled by alignment with a centering tool, spaced apart with shims and held in place by a nonconductive ceramic that is sintered onto the outer edge of the elements. This sintering of the elements to a ceramic structure is called a xe2x80x9cglass beading operation.xe2x80x9d The shim spacers are then removed to provide the electrically isolated elements of the electron gun. When thermionic emitters are used, a barium coated cathode is separately placed into the gun after this assembly operation. This is necessary because the fragile barium coating is not able to withstand the high temperatures at atmospheric pressure required in the glass beading operation.
One of the advantages of a field emission electron source is that the robustness of the cathode can allow the electron gun to be fully assembled before the glass beading operation. This eliminates the secondary step of inserting the thermionic component after the gun is assembled. A packaging technique is needed that takes advantage of the fact that the field-emission cathode can be placed at high temperature at atmospheric pressure without damage. The packaging should lower assembly costs of electron guns based on field emission cathodes. The package must also be constructed to allow precise alignment of the cathode in the electron gun. The structure resulting also should allow the use of the electron gun in a wide range of CRT neck-diameters.
An electron gun cathode assembly having a field-emitting cathode and a method for assembling are provided. The field-emitting cathode may be carbon-based. A non-conductive substrate, normally a ceramic material in the form of a disk, has electrical connection such as provided by a die region to the back of a field-emitter die. An emitting array has been grown on the die by known methods. Three field-emitting dies may be spaced on the substrate to form an electron gun for a color CRT. Electrical connections for the die and for electrodes integral with the cathode are made to conductive traces that are connected to pins that pass through the substrate. A disk or can having one or more apertures is spaced apart from the emitting array by a separate spacer ring or the spacing may be created by forming the disk or can. Normally the substrate, spacer and disk or can are joined by welding or brazing, by adhesive or mechanically. The cathode assembly, including the disk or can and spacer, can be aligned and also aligned with a separate focusing electrode with an aligning tool that fits in apertures in the disk or can and lens. The entire assembly can then be glass beaded using known techniques.